In an electric vehicle of the type employing lead-acid batteries, it is desirable for the driver to have a continuous reading of the state of charge of the batteries in the vehicle. One characteristic of lead-acid batteries is that the discharge curve of the batteries is not linear, that is, the terminal voltage of the batteries tends to remain fairly constant during initial discharge of the batteries when the batteries are discharged at a constant current draw, but the voltage tends to decrease relatively rapidly as the battery approaches its fully discharged state. Despite this characteristic of the batteries commonly used in an electric vehicle, it is necessary that the state of charge indicator provide an accurate readout of the charge remaining in the battery throughout the period of discharge of the battery.